This invention relates generally to air supply systems for gas turbine engines. More particularly, but not by way of limitation, this invention relates to an improved system for supplying compressed air for atomizing fuel in a gas turbine engine during the start-up cycle of the gas turbine engine.
Gas turbine engines are provided with integral service compressors that are driven by the gas turbine for supplying air to atomize the fuel. During start-up, the service compressor is running at such low speeds that the volume and pressure of air is insufficient to properly atomize the fuel. To alleviate this problem, starting compressors that are driven by separate motors at constant speeds have been provided to augment the air supply of the service compressors.
The use of the constant speed starting compressors has proved to be successful in providing the additional volume and pressure required. However, difficulty has been encountered with such systems when the output of the service compressor and the turbine compressor exceeds the capacity of the starting compressor. In an effort to eliminate this overloading problem, elaborate arrangements have been provided that include: sensors responsive to turbine speed to cut off the starting compressor drive motor; sensors arranged to sense either speed or pressure to isolate the starting compressor to prevent the overloads; and, a multiplicity of valves and the like that are manually operated to isolate the starting compressor and to shut down the starting compressor motor drive.
A certain degree of success has been obtained by the types of control systems mentioned hereinbefore. However, they are very complex or require considerable operator attention to be successful.
The object of this invention is to provide a very simple system incorporating a constant speed starting compressor to augment a service compressor during start-up of a gas turbine engine providing an adequate air supply for atomizing the fuel while automatically preventing damage to the starting compressor when the engine attains operating speed.